Net-Zero-Energy House Demonstrates Efficiency

A net-zero-energy house built by researchers in Maryland has produced more energy than it used last year and also demonstrated approximately 60 percent more energy efficiency than a similar house built to 2012 International Energy Conservation Code requirements, according to Builder.

The house was studied for a year by researchers at the National Institute of Standards and Technology in Maryland.

The four bedroom LEED Platinum house is 2,700 square feet and features a well-insulated building shell, energy efficient appliances, solar water heating and a solar photovoltaic system. The house was designed by Westford, Mass.-based Building Science Corp. and built by Therrien Waddell Construction.

According to Mark Davis of NIST, the most important difference between the house and a Maryland code-compliant home is the improvement in the thermal envelope — the insulation and air barrier. By nearly eliminating unintended air infiltration and doubling the insulation level in the walls and roof, the heating and cooling load was decreased dramatically.

The facility was considered both a laboratory and a house, and no humans were allowed in the house during the year of testing. Instead, mechanical controls and computer software in the attached garage simulated the behavior of a family of four.

Despite a winter that left the home’s photovoltaic and solar thermal panels covered with snow on 38 days, the house produced 13,577 kWhof energy, which was 491 kWh more than used by the house and its virtual occupants.

Although the renewable energy systems saved $4,373 in electricity payments over the year, front-end costs for solar panels, insulation, triple-paned windows and other technologies aimed at achieving net-zero energy performance were sizable.

In all, it has been estimated that incorporating all of the house’s energy-related technologies and efficiency-enhancing construction improvements would add about $162,700 to the price of a similar house built to comply with Maryland’s state building code. One focus of future research at the house will be ways to trim the cost difference.

However, while there have been a number of efforts in recent years to improve green efforts of new residential construction, the National Trust for Historic Preservation has argued that retrofitting old homes is better for the environment than building new ones.